This invention concerns Si-Al-O-N type materials and is more particularly concerned with the double phase Si-Al-O-N useful for the manufacture of cutting inserts used in metalworking.
There are numerous papers and patents describing the relatively new Si-Al-O-N materials which have been created by the addition of the aluminum and oxygen atoms to silicon nitride materials.
Most recently, these materials have found their way into the metalworking industry and have provided possibilities in the working of cast iron, nickel, based super alloys, and other similar substances.
More particularly, cutting inserts of a Si-Al-O-N type material made in accordance with U.S. Pat. No. 4,127,416, which is incorporated herein by reference, have proven to be useful in certain metal-working situations. The type of material made by the above-mentioned United States patent is manufactured as a predominantly single phase .beta.-Si-Al-O-N material with approximately 10 to 20 percent of a glassy phase present.
The material is made essentially as described in the patent which involves forming a polytype material as an initial step in the process. The polytype material may then be reacted with a controlled amount of silicon nitride and an oxide of yttrium, lithium or calcium to form a ceramic of at least 80, and preferably 95, percent being of a single phase .beta.-type Si-Al-O-N.
Such a material, when produced, has a transverse rupture strength in the range of 100,000 to 110,000 pounds per square inch using the procdure described in later examples and a knoop hardness in the range of 1450 to 1800 kilograms per square millimeter at 100 grams load.